Psoriasis. Unless you don't mind someone with dry, peeling, cracking and bleeding hands leaving behind their DNA on the bars.
There is a condition where people sweat excessively from their hands. This could be a safety hazard if a bar slips out of their hands.
I've been working out for 25 years and have never seen someone wearing gloves with psoriasis at any of the gyms I've been to. How do I know, because seeing the same people in gloves, they take them off when leaving the gym and arrive to the gym without them on. I've seen people with skin conditions on their hands and you can spot it from far away.
But sometimes, there are a few who do wear them outside the gym after and before working out, as I've seen them walking on the street with their gloves on. So these few, I've never seen their barehands.
I sweat excessively from my hands and don't use gloves. Gloves were a fad in the 90's, but since early 2000's the amount of people wearing them have been greatly reduced year after year (excluding females). Went to the gym yesterday and full house, not 1 glove wearer.
I did see 1 guy a few weeks ago wearing surgical gloves. But he was also wearing a N-95 mask and goggles, so I doubt he' has a skin condition.
People workout all the time with skin conditions and go skin on bare metal. Especially ring worm. Which is why I clorox wipe everything before I touch it. And get a good # of guys who no wash their hands after taking a piss/shit. I see them walk right out without hitting the sink area.